Rails Polymorphic Children

Question

I've seen many good examples of a child model (say, a 'Comment') belonging to multiple parent models ('Post', 'Product', etc). Here is one, for example: http://railscasts.com/episodes/154-polymorphic-association.

I am looking to accomplish the opposite however, where a parent has multiple polymorphic children. A classic example would be an 'ActivityFeed' that has multiple types of children ('Photo', 'Comment', etc).

How would one go about modeling this relationship in Rails?

Answer 1

You'd probably want to use some sort of intermediate record, say ActivityItem, that sits between the ActivityFeed and the Photo, Comment, etc...

class ActivityFeed < ActiveRecord::Base
  has_many :activity_items
end

class ActivityItem < ActiveRecord::Base
  belongs_to :activity_feed
  belongs_to :item, :polymorphic => true
end

class Photo < ActiveRecord::Base
  has_many :activity_items, :as => :item
end

class Comment < ActiveRecord::Base
  has_many :activity_items, :as => :item
end